A Simple Collision Method

[JulianDave]

I don't know if this has been posted before, but this is an easy way to do collisions. It will only work in some applications, but it's a good thing to file away until needed. You just calculate the distance between the player and all of the other objects it could collide with to see if they get too close. I usually pick a point that is the center of the object. Then compare distances to see if anything gets within a set distance. Just play with this value to get something realistic. This won't work, for example, if the objects very in size, unless you add a little more complexity by keeping a custom distance for each object in an array. Performance wise, I don't know how bad this is, but it's fairly straight forward.

distance = Math.Sqrt(Math.Pow(PlayerPosition.X - AlienPosition[i].X, 2) + Math.Pow(PlayerPosition.Y - AlienPosition[i].Y, 2));

I am using this in a newer version of aMAZEing that I haven't released yet and it works great.

You can also use this to vary how objects move in relation to the player. For example, a "ball of death" that is attracted to a player picks random directions to move and compares the distance to the player vs. it's current distance. It then chooses a direction that gets it closer to the player.

Dave

[Red Sky]

Based off of what you are saying, it would seem that a distance equal to half the width of the 'player' would be a good 'set distance', since you are going from the center of the 'player'. Also, your 'ball of death' is sort of like how the red ghost in pacman works. He always aims for 2 spaces ahead of pacman, and that dictates his movement.

[JulianDave]

Originally Posted by Red Sky

Based off of what you are saying, it would seem that a distance equal to half the width of the 'player' would be a good 'set distance', since you are going from the center of the 'player'.

You have to add half the width of the player with half the width of the object. They would then be just touching. Now that I think about it, this could be done by adding .Height or .Width after the sprite texture to get the specifics of each object, without an array that keeps track of that.

Dave

[Red Sky]

Yep. Yay for Texture2Ds built in properties.

[DiNoGames]

Originally Posted by JulianDave

distance = Math.Sqrt(Math.Pow(PlayerPosition.X - AlienPosition[i].X, 2) + Math.Pow(PlayerPosition.Y - AlienPosition[i].Y, 2));

There are built-in functions to calculate distances of several types like:

- float MathHelper.Distance(float, float) (to get the non negative distance between two values)
- several overloads of Vector2.Distance (to get the distance between two 2D positions)
- several overloads of Vector3.Distance (to get the distance between two 3D positions)

You can also use BoundingSpheres for the purpose you are explaining here. BoundingSpheres and BoundingBoxes have built-in collision detection routines.

So your calculation is a good start, but XNA has all this stuff built in. You don't have to reinvent the wheel

[JulianDave]

Thank you for posting that. I'll have to get a little more familiar with all of the built-in functions.
Dave

[Netrix]

You could also create Rectangles that have the same positions and sizes as the relevant textures and use the built-in function to determine if they collide or not. Though, this is limited in that it only works for rectangles.

Rectangle player, thing;
 
//Initalize the positions and sizes.
 
Boolean collides = player.Intersects(thing);